Probascar only relocates where the outcome of the battle would be. Instead of moving into a space, he moves creatures into his. If I remember correctly this means a creature still will be able to defend, and then is relocated into probascar's space.

Oh um yea... lol I'll keep the rest of this post for people who might be interested. I just realized the question after I wrote everything else.

Hmm maybe I'm not understanding what your asking. Here's the scenario I was picturing:

If Proboscar would move into an opposing Creature's space it relocates that opposing Creature into Proboscar's space instead.

You declare an attack using Probascar on an opposing creature. The opponent chooses to defend. The defending creature will switch places with the creature you had originally declared an attack on. And combat takes place on Probascar's original space (so the winner goes to where Probascar originally was).

Are you asking instead that the opponent has a Probascar that has defender? If so, then he defends as normally and combat plays out as normal. His ability doesn't doesn't do anything since he's not declaring combat.